(a) Field of the Invention
The present invention relates to a display device having an anisotropic-conductive adhesive film and, more particularly, to a display device including a display panel and a flexible wiring member bonded onto the display panel by using an anisotropic-conductive adhesive film.
(b) Description of the Related Art
Display devices, such as a LCD device, include a display panel and a drive unit including a driver IC electrically coupled to the display panel for driving the display panel. The drive unit includes a flexible wiring substrate or flexible wiring member, on which the driver IC is mounted using a tape-automated-bonding (TAB) technique. The flexible wiring member, on which the driver IC is fixed, is coupled at an end thereof onto an edge portion of the display panel, and is folded onto the rear surface of the display panel for mounting the driver IC on the rear side of the display panel. This configuration reduces the planar size of the resultant display device.
FIG. 12 shows a sectional view of a conventional LCD device, as a typical example of the display device, which includes a LCD panel and a flexible wiring member bonded onto the LCD panel. The LCD panel 10 includes an active-matrix substrate 11 on which an array of active devices such as TFTs (thin-film transistors) are formed, a color-filter substrate 12 opposing the active-matrix substrate 11, and a liquid crystal (LC) layer (not shown) sandwiched between the active-matrix substrate 11 and the color-filter substrate 12. An edge of the active-matrix substrate 11 protrudes from the corresponding edge of the color-filter substrate 12, and a plurality of terminals (first terminals) 16 are formed in the vicinity of the edge of the active-matrix substrate 11.
The flexible wiring member 20 includes a base substrate or base film 21, a plurality of wires 22 formed on the base substrate 21, and an overcoat film 23 covering the wires 22 on the base substrate 21. The overcoat film 23 terminates at the location which is D3 distance apart from the edge of the active-matrix substrate 11, whereby the wires exposed from the overcoat film 23 configure exposed terminals (second terminals) 24 in the vicinity of the end of the flexible wiring member 20.
The flexible wiring member 20 is bonded onto the LCD panel 10 by an anisotropic-conductive adhesive film (ACF) 30 sandwiched between the terminals 16 (first terminals) of the LCD panel 10 and the terminals (second terminals) 24 of the flexible wiring member 20. The ACF 30 is such that conductive particles 32 are dispersed in insulating resin 31 having a thermo-setting or thermoplastic property, whereby the insulating resin 31 mechanically fixes the second terminals 24 onto the first terminals 16, and the conductive particles 32 electrically connect the second terminals 24 to the first terminals 16.
Upon coupling the flexible wiring member 20 onto the LCD panel 10, the ACF 30 obtained by filming anisotropic-conductive adhesive is sandwiched between the first terminals 16 and the second terminals 24 for temporarily fixing thereof and then subjected to a thermo-compression bonding process. In the thermo-compression bonding process, the insulating resin is cured when the ACF 30 is being compressed so that the conductive particles contact both the terminals 16 and 24. The connection bonding using the ACF 30 obviates connection of individual terminals 24 to respective terminals 16, thereby simplifying connection of the terminals.
If there is a level difference or step difference in the area of the ACF 30 during the connection boding using the anisotropic-conductive adhesive, the step difference may impede fluidity of the conductive particles 32. This may cause an alignment of the conductive particles in contact with one another along the extending direction of the edge of the step. For example, if the distal edge 25 of the overcoat film 23 is located in the vicinity of the edge 17 of the active-matrix substrate 11 or inside of the edge portion of the active-matrix substrate 11, as shown in FIG. 13, the fluidity of the conductive particles 32 is impeded by the edge 25 of the overcoat film 23, thereby causing the conductive particles 32 to align with one another in the extending direction of the edge 25 of the overcoat film 23. The alignment of the conductive particles 32 in contact with one another will cause a short-circuit failure between adjacent terminals.
For avoiding the short-circuit failure caused by the alignment of the conductive particles, it is necessary to secure a sufficient distance D3, as shown in FIG. 12, between the edge 17 of the active-matrix substrate 11 and the edge 25 of the overcoat film 23 in the conventional technique. The sufficient distance D3, however, may allow a foreign object or foreign particle to be attached onto the exposed wires or may cause corrosion of the exposed wires 22 in the flexible wiring member 20. This may also cause a short-circuit failure.
For avoiding the short-circuit failure between adjacent terminals, another insulating film may be formed on the exposed terminals 24; however, it increases the process steps and raises the cost of the LCD device.
Patent Publication JP-2004-118164A describes a technique for solving the above problem, wherein the overcoat film protrudes within the space between adjacent terminals to expose the terminals, and the ACF is formed in the entire area of the exposed terminals.
The technique described in the patent publication suppresses the short-circuit failure caused by the alignment of the conductive particles because the conductive particles are distributed along the extending directions of the three edges of the protrusion of the overcoat film. However, reduction of the pitch of the terminals in the current semiconductor devices makes it difficult to employ the configuration of the overcoat film having the protrusion in the space between adjacent terminals while exposing the terminals.